Two animal models for studying the virulence of Entamoeba histolytica have been published and the description of a unique beaded virus of E. histolytica is in Press. In a collaborative study Dr. M.P. Valsamus has investigated the pathogenesis of the hydrocephalus observed in some animals following the intracerebral inoculation of newborn mice. We have investigated the virulence of clones of E. histolytica obtained by microisolation, and a possible role of viruses of E. histolytica in a phage-like conversion of virulence was examined. A new and rapid in vitro test of virulence of E. histolytica is being developed and shows promise for distinguishing strains of amebae of different virulence for newborn hamster liver within 2 to 3 hours. BIBLIOGRAPHIC REFERENCES: Mattern, C.F.T. and Keister, D.B. Experimental Amebiasis I. Pathogenicity of Axenically cultivated Entamoeba histolytica in the brain of the newborn mouse. Amer. J. Trop. Med. and Hyg. 26: 393-401, 1977. Mattern, C.F.T. and Keister, D.B. Experimental Amebiasis II. Hepatic amebiasis in the newborn hamster. Amer. J. Trop. Med. and Hyg. 26: 402-411, 1977.